1. Field of the Invention
This document relates to a backlight unit and a liquid crystal display using the same capable of improving a heat emission characteristic.
2. Discussion of the Related Art
A liquid crystal display (“LCD”) has been widely applied due to its lightweight, thin profile, lower power consumption driving, and so on. Such an LCD has been employed as a portable computer such as a notebook PC, an office automation device, an audio/video device, an indoor/outdoor advertisement display device or the like. A transmissive LCD which takes up most of the LCDs displays images by controlling an electric field applied to an LC layer to adjust a light from a backlight unit depending on data voltages.
As a light source of the backlight unit, a light emitting diode (LED), which has the advantages of low power consumption, light weight and high luminance, has been suggested instead of a fluorescent lamp such as a cold cathode fluorescent lamp (CCFL).
The LED has good characteristics, for example, small-sized, clear light-emission, good initial driving, quake-proof, and strong durability in frequent light-on/light-off. In recent years, with the advent of a white LED which emits a white light, application fields of the LED has been widespread from indicators of electronic products, to households, panels for advertisement, or the like. Furthermore, in accordance with a high efficiency of an LED package, the LED is applied to streetlights, head lamps for automobiles, and general illumination light sources replacing fluorescent lamps.
For energy applied to the LED package, about 15% thereof is converted into a light and about 85% thereof is consumed as a heat. The efficiency and lifespan of the LED package are reduced as a heat generated from the PN junction becomes more. Therefore, a high efficiency and high luminance LED package requires a heat emission design for dissipating heats generated from the LED chips.
As shown in FIG. 1, an LED package 1 is soldered on a generally expensive metal PCB (printed circuit board) 2 for heat emission. The metal PCB 2 has a structure in which a resin layer 2B, a copper layer 2C, and a solder resist layer are stacked on an aluminum metal substrate 2A. The resin layer 2B functions to electrically separate the copper layer 2C where currents flow from the underlying metal substrate 2A, and also functions to form a heat transfer path between the copper layer 2C and the underlying metal substrate 2A. A heat generated from the LED package 1 is first transferred to the copper layer 2C, and then to the underlying metal substrate 2A via the resin layer 2B. The heat transferred to the metal substrate 2A is transferred to a bottom cover 4 of the backlight unit via a heat emission pad 3 attached to the backlight unit. The bottom cover 4 takes up a relatively large area, and thereby can sufficiently function as a main heat emission plate.
However, as can be seen from the above heat transfer process, in the related art, the heat transfer path is complicated and particularly the heat transfer efficiency is very low due to the resin layer and the heat emission pad having lower heat conductivity than metal. As a result, there is limitation in improving the heat emission characteristic of the LED package in the related art.